Sludge liquefaction process and agents

ABSTRACT

The invention involves the demulsification and liquefaction of hydrocarbon based sludges. A demulsifier and a liquefaction agent and methods of using the same are disclosed. In a preferred embodiment, the demulsifier contains a salt of DDBSA, polypropylene glycol, and citrene. In a preferred embodiment, the liquefaction agent contains a glycol ether and sodium silicate. In another preferred embodiment, the liquefaction agent contains a glycol ether and citrene. In preferred practice, the sludge is treated with the liquefaction agent, circulated, treated with the demulsifier, and circulated further. An object of the invention is to provide a hydrocarbon based sludge that is sufficiently liquefied to be pumped and which is sufficiently demulsified to allow the waters, oils, and solids in the sludge to separate.

CONTINUATION

This application is a division of allowed application Ser. No.08/733,527, filed Oct. 18, 1996, now U.S. Pat. No. 6,120,680, which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to liquefaction and demulsificationagents for hydrocarbon based oil sludges and to their use to facilitatethe demulsification and liquefaction of hydrocarbon based oil sludgesand more particularly to their use to facilitate the demulsification andliquefaction of sludges in storage tanks.

2. Prior Art

Hydrocarbon based oils such as petroleum oils or vegetable oils areoften stored in tanks. Over time, ‘sludge’ forms in the bottom of thesetanks. Sludge is a mixture of deposits that collect at the bottom of thetanks. The sludge can be distinguished from oil in the tank primarily bya difference in viscosity. The minimum viscosity for a sludge varieswithin the industry from as low as 100 centipoise to as high as 500centipoise.

The composition of the sludge varies from tank to tank and will dependupon the composition of the oil or oils that have been stored in aparticular tank. The components of the sludge can generally be brokeninto three groups: water and water soluble materials (waters); oils andoil soluble materials (oils); and solids. The solids generally becomewetted with either oils or waters. The sludge is formed when thesecomponents emulsify. (The more technically correct term for asolid/liquid colloid is “sol.” However, for the sake of convenience,emulsion is used herein to refer to both liquid/liquid and tosolid/liquid colloids)

Over time, the heavier elements in the oil such as paraffins,asphaltenes and solids migrate to the bottom of the tank and enter thesludge. As the concentration in the sludge of these heavier componentsincreases, the sludge becomes more viscous and, depending upon thesludge components, may even solidify. The sludge becomes problematicwhen its viscosity prevents it from being pumped, and it begins to buildup at the bottom of the tank. Eventually these sludges must be removed.If left unchecked, the sludge formation, will adversely impact thecapacity of the tanks. However, removal of these sludges poses anexpensive and sometimes dangerous problem for those in the tank farmindustry.

In one removal method, these sludges are treated with aromatic compoundssuch as toluene to dissolve them. These chemicals have severalshortcomings. First, the aromatic compounds are generally soluble in oilbut not in water. This makes it difficult for the aromatics toeffectively liquefy sludge which contain any substantial amount ofwater. Second, these chemicals are poor demulsifiers, so the liquefiedsludge is still an emulsion. Introduction of demulsifiers into thesludges that have been liquefied aromatically has been found to lead topoor results. This is believed to result from the aromatic's inabilityto form a solution with the waters in the sludge. The failure toeffectively place the waters into solution is believed to inhibit theability of the demulsifiers to interact with the emulsified particlesand thus to break the emulsion. Third, these chemicals often have healthand safety problems associated with them. Many aromatic compounds arehighly flammable and some are known carcinogens. This latter trait cansubstantially increase the disposal expenses of sludges that have beenaromatically liquefied.

In another method, heat is applied to the sludge, usually with steam.This process also provides less than satisfactory results. Some sludgesare not readily susceptible to liquefaction through heating. Onceliquefied, the sludge must be pumped before it cools because coolingusually results in the reformation of a solid or semi-solid sludge.Cooling in the pump lines can lead to blockages which can be quitedifficult to clear. Sludge that is removed using heat is often difficultto remove from the receiving vessel without reheating it. Heating thesludge can also cause some sludges to emit vapors which may create afire hazard or a health hazard.

A third option is manual removal. This method is time consuming andexpensive. The men that work in the tank are exposed to potential healthrisks connected with the chemicals in the tank as well as to possibleinjury in the fires or explosions that are a constant concern in thepetroleum industry. Despite these drawbacks, manual removal is the onlyfeasible removal mechanism for many sludges. Even when the previouslydiscussed methods are employed, the sludge is often not renderedsufficiently fluid to be pumped out of the tank and at least someportion must be manually removed.

Removal of sludge manually is often very labor intensive, and can takeas much as 180 days to clean a single tank. This results in lost revenueto the tank farm due to diminished storage capacity during this period.The labor requirements can often push the cost of cleaning a single tankover $(US) 500,000.00.

All of the previously discussed sludge removal methods share a commonshortcoming: the loss of commercially valuable hydrocarbons contained inthe sludge. The oils that are trapped in the sludge often havecommercial value, but because of their emulsified state, it is notfeasible to refine them. Consequently, these sludges must be discarded.This results in a double loss to the tank farm operator. First, he mustthrow away the unusable hydrocarbons trapped in the sludge. Second, thesludge is frequently treated as hazardous waste and can be expensive todispose.

Accordingly, a demulsifier, a liquefaction agent, and method for usingthe same are desired to meet the following objectives.

OBJECTS OF THE INVENTION

It is an object of the invention to liquefy hydrocarbon sludge.

It is another object of the invention to demulsify hydrocarbon sludge.

It is another object of the invention to provide a refineablehydrocarbon stream from a liquefied demulsified hydrocarbon sludge.

It is another object of the invention to liquefy hydrocarbon sludge in aminimal amount of time.

It is another object of the invention to liquefy hydrocarbon sludgeusing a minimal amount of liquefaction agent.

It is another object of the invention to demulsify hydrocarbon sludge ina minimal amount of time.

It is another object of the invention to demulsify hydrocarbon sludgeusing a minimal amount of demulsifier.

It is another object of the invention to provide a liquefied hydrocarbonsludge which may be removed with a minimal amount of human interactionwith the sludge or the liquefaction agent.

It is another object of the invention to provide a demulsifiedhydrocarbon sludge which may be removed with a minimal amount of humaninteraction with the sludge or the demulsifier.

It is another object of the invention to liquefy hydrocarbon sludgewithout using heat.

It is another object of the invention to provide a non-toxic agent forthe liquefaction hydrocarbon sludge.

It is another object of the invention to provide a non-toxic agent fordemulsifying hydrocarbon sludge.

SUMMARY OF THE INVENTION

There are demulsifiers known in the art which are capable of breakingthe emulsions in hydrocarbon sludge. One such demulsifier is dodecylbenzyl sulfonic acid (DDBSA). A preferred embodiment of this demulsifierare its salts and most preferably its amine salts, all of which arewater and oil soluble. The inventor purchases his DDBSA from Witco(address given below) and produces amine salts of DDBSA with amines madeby Texaco Chemical Company, P.O. Box 27707, Houston, Tex. 77227, andsold under the trade name C-6 Amine. The invention comprises aliquefaction agent which facilitates the action of the demulsifier byliquefying the sludge and methods of using the same. As the sludge isrendered more fluid, the demulsifier is better able to attack theemulsified particles. As the emulsions are broken the phases separateand liquidity is restored. The result is a flowable end product that isseparated into solids, waters, and oils. The oils and the waters may bepumped out separately, and if desired the oils may be refined. Only thesolids need to be removed mechanically.

As noted, the invention works by increasing the liquidity of the sludgewhich allows the demulsifier to work more effectively. Breaking theemulsions also has a liquefying effect upon the sludge. In this way, theliquefaction agent and the demulsifier work together synergistically.This allows a flowable end product to be produced with a minimal amountof liquefaction agent and demulsifier.

The invention comprises the use of two primary liquefaction agents. Thefirst are the glycol ethers {CH₂OH—CHOH—O—R}. These chemicals are anexcellent choice for the liquefaction agent because they have thesomewhat uncommon property of being soluble in water and in oil. Thus,they are able to form a solution with both the waters and the oils inthe emulsion and to disperse the emulsified particles within thesolution. Once the emulsified particles are dissolved, or at leastpartially dissolved, and dispersed the demulsifiers can more easilyobtain access to the particles and break the emulsion. The particularglycol ether tested by the inventor was ethylene glycol butyl ether,{CH₂OH—CHOH—O—C₄H₉}.

Polymerized glycol ethers, H{—O—CHOH—CHOH—}_(n)OH, are anotheracceptable liquefaction agent. Like the monomers, they are soluble inwater and in oil and can thus liquefy and disperse the emulsifiedparticles. They have advantages over the monomer in that they aregenerally cheaper to manufacture and are generally less toxic than themonomers. The particular polymerized glycol ether which has been tested,poly (oxy-1,2 ethanediyl), α butyl Ω hydroxy,H{—O—CH(C₄H₉)—CHOH—}_(n)OH, outperformed the monomer in liquefaction anddispersion. This polymer is a by-product produced in the manufacture ofethylene glycol butyl ether. It is frequently considered a wasteproduct, although the inventor is aware of its use as a brake fluid. Itis available from Occidental Chemical Corp. (OxyChem) Occidental Tower,P.O. Box 809050, Dallas, Tex. 75380 and from Dow Chemical Company,Midland, Mich. 48667 under the trade names Glycol Ether Residue andGlycol Ether Bottoms respectively.

The second primary liquefaction agents are the polyalkylene glycols,H{O(CH₂)_(X)}_(n)OH. They also are soluble in oil and in water and arethus effective liquefaction and dispersion agents. Polyalkylene glycolshaving molecular weights of between about 250 and about 2500 areexpected to provide the best result. Polyalkylene glycols with amolecular weight below about 250 are generally expected to beinsufficiently oil soluble to perform adequately. They are alsogenerally more toxic than the higher molecular weight polymers.Polyalkylene glycols with a molecular weight above about 2500 aregenerally expected to be too viscous to effectively enter into solutionwith the sludge.

A particular polyalkylene glycol which has been shown to performadequately is polypropylene glycol. H{OCH₂CH₂CH₂}_(n)OH. Although otherpolyalkylenes glycols would be acceptable liquefaction agents, theresiduals of some—such as polyethylene glycol and polybutyleneglycol—are hazardous. Polypropylene glycols are preferred because theirresiduals are not hazardous. Off-specification products will generallybe used where possible because of their cost advantages over thespecification grade products. Use of the polypropylene glycols willfacilitate the use of the cheaper off-specification products. A slightlyoff-specification quality polypropylene was used during testing. It hadan average molecular weight of between 950 and 1,200. As will beillustrated in the discussion of the experiments below, it performedquite well and should provide an economical commercial substitute forspecification quality polypropylene.

These liquefaction agents and demulsifiers may be used in combinationwith other agents to optimize the results obtained. Some of these otheragents are discussed below.

A high paraffin and/or asphaltene content will make the sludge veryviscous. If enough paraffins and/or asphaltenes are present, the sludgemay actually solidify and can become quite hard. In such sludges, it isgenerally desirable and may be necessary to soften the sludge so thatthe demulsifiers and the liquefaction agents can enter the sludge. Tosoften the sludge, it should be treated with a plasticizer, such asterpene. Terpenes, {CH₁₀H₁₆}, are oil soluble, water insoluble compoundswhich are distilled from plants. Of principal relevance to the presentinvention is their ability to dissolve paraffins. By dissolving, orpartially dissolving, the paraffins, the terpenes can soften the sludgesufficiently to allow the demulsifiers and the liquefaction agents toenter.

Many terpenes are toxic; however, citrene, a terpene extracted fromcitrus rinds, is not toxic and is a good plasticizing agent. Citrene is,therefore, preferred over the other terpenes as a plasticizer. Inaddition to their toxicity, most terpenes are also flammable. Citrene,for example, has a flash point of 120° F. The terpenes may be used moresafely by mixing them with a liquefaction agent. For example, a 1:1mixture by volume of citrene and poly (oxy-1,2 ethanediyl), α butyl Ωhydroxy has a flash point of 180° to 200° F. While this is no longerconsidered flammable, it is still considered combustible and it shouldbe handled accordingly.

Another agent which may be used in combination with the demulsifiers andliquefaction agents is sodium silicate which may be used to facilitatethe separation of solids from the sludge. The sodium silicate helps tobreak the adhesion between the oils and the solids and forms a coatingon the solid particles. The coating prevents the oils from readhering tothe solids and encourages gravity separation of the solids from thesludge.

Another agent which may be added to the demulsifiers and liquefactionagents is a blend of resin esters and glycol esters. This agent is addedprimarily to effect the separation of the finer solid particles from thesludge. Additionally, it is useful in completing the separation of thewaters from the emulsion. This agent may be thought of as a “polishing”agent in that its function is primarily to remove the last of the solidsand the waters from the almost fully separated emulsion. Its compositionbeyond that listed above is unknown. It is an oil soluble but waterinsoluble product sold by Witco Corp. of 3200 Brookfield (Almaeda Rd.),Houston, Tex., under their trade names DRE8164 and DRG162.

In some applications it may be desirable to add an acid to the sludge.First, the inventor has noticed a mild increase in the effectiveness ofthe liquefaction agents and demulsifiers when their pH is acidic.Second, the addition of the acid can have positive effects on the costof disposing the waters separated from the sludge. Many of the agentsdiscussed above have a pH which is quite basic. As a result, the watersproduced in the demulsification process will be basic as well. Theirbasicity can increase the cost of disposal because of the environmentalproblems associated with high pH waste water. Addition of an appropriateamount of acid can lower pH to acceptable levels. The inventorcontemplates using citric acid as the acid additive because it isnon-toxic. However, for purposes of lowering pH, other acids areacceptable.

Use of the acid agent will usually be undesirable in petroleum sludgesbecause most petroleum sludges contain iron sulfides. The acids willreact with the iron sulfides to produce hydrogen sulfide, a highlypoisonous gas. This will not be a problem when the invention is used toseparate sludges that do not contain sulfides, such as vegetable oilsludges.

In operation, the liquefaction agent or agents and the demulsifier willbe added to the sludge. The other agents discussed above may be added aswell. The sludge and added components will be mixed together andrecirculated for several hours. The agents will act upon the sludge,causing it to liquefy and to demulsify. Upon completion of the process,the sludge will separate into an oil layer, a water layer and a solidlayer. The liquids may be removed and easily separated. It isanticipated that the oils extracted from the sludge will be refineablein most cases. The waters will usually be treated and discarded. Thesolids will require mechanical removal from the tank and will alsousually be discarded. The preferred mode of effecting these steps isdiscussed in more detail in the following sections.

DESCRIPTION OF THE BEST MODE

The inventor contemplates using the invention in five differentformulations. These are referred to for convenience as C105 BC, C105 AC,C105 SA, C105 EB, and C105 EBS. The composition for each of these isgiven below. All percentages are by volume and are intended to beapproximations only and not limiting in any sense.

C105 BC NaSi  5% glycol ether  5% [preferably poly (oxy- 1,2ethanediyl), α butyl Ω hydroxy] water 90% C105 AC add citric acid  1%[solid concentrate pH < 1] to C105 BC C105 SA glycol ether 50%[preferably poly (oxy- 1,2 ethanediyl), α butyl Ω hydroxy] terpene 50%[preferably citrene] C105 EB amine salt of DDBSA 60% polyalkylene glycol15% [preferably polypropylene glycol M.W. ≈ 950 to ≈ 1200] blend ofresin esters 12.5%   and glycol esters [preferably DRE8164 (10%) andDRG162 (2.5%) Witco, Corp.] terpene 12.5%   [preferably citrene] C105EBS C105 EB 10 to 40% C105 SA 90 to 60%

In practice, either the C105 AC or the C105 BC will usually be appliedfirst, followed by the C105 EB. If the paraffin content is high, theC105 SA or C105 EBS should be used first, again followed by the C105 EB.To facilitate the selection of which formulations of the inventionshould be used, the operator should first obtain a sample of the sludge.Paraffin content could be measured directly from the sample; however, itwill usually be more convenient to measure viscosity as the viscositywill largely be a function of the paraffin content and of the molecularweight of the particular paraffins.

For sludges with a viscosity of less than about 1500 centipoise, theC105 BC or C105 AC will usually be an acceptable liquefaction agent.Sludges with a viscosity of between about 1500 and about 5000 centipoisewill usually respond better to treatment with some C105 SA or C105 EBSliquefaction agent. However, it should be noted that in the examplesdiscussed below, a sludge having a viscosity of approximately 4000centipoise was effectively treated using only C105 BC and C105 EB.Sludges with a viscosity above about 5000 centipoise will usuallyrequire initial treatment with a C105 SA liquefaction agent. In allcases, treatment with a C105 EB demulsifier will follow the initialtreatment. The only exception being the case where the C105 EBS has asufficiently high C105 EB content that addition of further C105 EB isnot necessary.

When the C105 BC or C105 AC liquefaction agents are used, the inventorexpects an addition of a volume of the liquefaction agent equal to aboutone (1) percent to about ten (10) percent of the total sludge volume tobe sufficient, and expects a volume of about six (6) percent to beappropriate in most cases. When the C105 SA liquefaction agent is used,the inventor expects an addition of a volume of the liquefaction agentequal to about two and one half (2.5) percent to about thirty (30)percent of the total sludge volume to be sufficient, and expects avolume of about five (5) percent to about ten (10) percent to beappropriate in most cases. When the C105 EBS liquefaction agent is used,the inventor expects an addition of a volume of the liquefaction agentequal to about one half of one (0.5) percent to about ten (10) percentof the total volume of the sludge to be sufficient, and expects a volumeof about two and one half (2.5) percent to about five (5) percent to beappropriate in most cases. When the C105 EB demulsifier is used, theinventor expects an addition of a volume of the demulsifier equal toabout one half of one (0.5) percent to about one and one half (1.5)percent of the total volume of the sludge to be sufficient, and expectsa volume of about one half of one (0.5) percent to be appropriate inmost cases.

In many cases where the C105 SA or C105 EBS is used, the amount neededmay be reduced by using either liquefaction agent in combination withthe C105 BC liquefaction agent. This is especially beneficial from acost perspective. Of the different formulations, C105 BC and C105 AC arethe least expensive. The C105 SA is considerably more expensive. TheC105 EBS and the C105 EB are more expensive still. Use of the C105 BC toreduce the amount of C105 SA or C105 EBS needed can reduce the overallcost of treatment.

It must be emphasized that each sludge is different. The variety ofsludge compositions requires that some trial and error lab work beperformed on small sludge samples to determine the exact combination offormulations that would be best to liquefy and demulsify any particularsludge.

In some applications, it may be desirable to minimize the amount ofdemulsifiers or liquefaction agents that enter the waters in the sludge.It is often necessary to treat these waters before they are disposed,and the removal of any additional chemicals contained in the water willincrease the cost of that treatment. However, several of the chemicalsused as liquefaction agents or as demulsifiers are soluble in oil andwater. When these agents are added to the sludge, some of them willultimately end up in the waters. The amount in the waters can beminimized by placing the agents in solution with water insolublechemicals prior to their introduction into the sludge. The waterinsoluble chemicals are believed to buffer the ability of the watersoluble chemicals to go into solution with the waters. For example, thiswill result in the water stream removed from a sludge treated with C105SA or C105 EBS containing fewer glycol ethers than the water stream froma similar sludge treated with C105 BC. Although it will increase thecost of treatment, it may be desirable in some instances to treat evensludges with viscosities of less than 1500 centipoise with liquefactionagents that consist of only C105 SA or C105 EBS.

When used to treat sludge in storage tanks, the different formulationsof the invention may be introduced through the tank's loading anddrainage pipes. In a preferred mode of operation, pumps are added sothat the formulations may be added under pressure. Delivering thedemulsifiers and liquefaction agents under pressure allows them tophysically penetrate more deeply within the sludge which in turn allowsthe sludge to be treated more rapidly. Pressures of 40 to 120 p.s.i.have been found to be effective.

In operation, the formulations are added to the sludge under pressurethrough the tank's loading pipes. The excess fluid is then pumped out ofthe tank's drainage pipes, recirculated by the pump back into theloading pipes, and reintroduced into the tank under pressure. As theprocess is repeated and the sludge becomes more fluid, the liquefiedsludge will join the excess fluid and will be recirculated itself. Thisleads to a thorough mixture of the demulsifiers and liquefaction agentswith the sludge which in turn leads to a thorough treatment of theentire sludge.

The most preferred mode of administering the formulations of theinvention contemplated by the inventor would entail injecting theformulations into the sludge under pressure through a plurality ofextensible nozzles extending down from the top of the tank. This wouldallow the formulations to be introduced into the sludge evenly andshould lead to quicker demulsification and liquefaction with theintroduction of less of the respective agents. As in the previous modeof administering the formulations of the invention, the excess fluidwould be pumped out through the drainage pipes, recirculated by thepumps and reintroduced to the tank via the nozzles. The inventoranticipates that a pressure of 150 to 500 p.s.i would be preferable inthis mode of operation.

EXAMPLES

In the following examples, the glycol ether in the C105 BC was in theform of Glycol Ether Residue obtained from Oxychem which was over 90%poly (oxy-1,2 ethanediyl), α butyl Ω hydroxy, and the polyalkyleneglycols were in the form of an off specification polypropylene glycolhaving an average molecular weight of between about 950 and about 1200.

Example 1

The invention was used to treat a crude oil storage tank having a totalvolume of approximately 200,000 bbl and containing approximately 25,000bbl of sludge. A sample was taken revealing that the sludge containedabout 56.7% by weight oils and about 43.3% by weight waters. Containedwithin the waters were about 7.5% by volume solids. The sludge had aviscosity of about 4000 centipoise.

Approximately 1500 bbl of C105 BC (˜6% of the sludge volume) were addedto the tank over six hours. Recirculation at approximately 8000 bbl perhour was conducted while the C105 BC was being introduced. Approximately125 to 160 bbl of C105 EB (˜5000 ppm) were then added. Recirculation wascontinued for forty-eight hours at approximately 8000 bbl per hour. Atthe end of the forty-eight hours, the sludge was liquefied anddemulsified. An oil layer and a water layer having a combined volume ofapproximately 24,500 bbl was pumped off. A solid layer comprisingprimarily sand and anhydrite remained. The solid layer had a volume ofapproximately 500 bbl. Waters were of course contained within the solidlayer. These waters were siphoned out and the solids were mechanicallyremoved.

The liquids extracted from this tank were disposable as oil field wasteunder the EPA's solid waste disposal regulations. No waste wasclassified as hazardous waste. The total volume of the demulsifiers andliquefaction agents used to treat the sludge was less than 1700 bbl.This amounted to less than 7% of the total volume of sludge treated.Finally, the total down time for the tank was only 6 days.

Example 2

The invention was used to treat a crude oil storage tank having a totalvolume of approximately 200,000 bbl and containing approximately 31,000bbl of sludge. The sample data taken from the sludge in example one wasused in treating the sludge in this example.

Approximately 1900 bbl (˜6% of the sludge volume) of C105 BC were addedto the tank over eight hours. Recirculation at approximately 8000 bblper hour was conducted during the introduction of the C105 BC. When allof the C105 BC had been added approximately 155 to 165 bbl (˜5000 ppm)of C105 EB were added to the tank. Recirculation was continued forforty-eight hours at approximately 8000 bbl per hour. At the end of theforty-eight hours, the sludge was liquefied and demulsified. An oillayer and a water layer having a combined volume of approximately 30,850bbl were pumped off. A solid layer comprising primarily sand andanhydrite remained. The solid layer had a volume of approximately 150bbl. Waters were of course contained within the solid layer. Thesewaters were siphoned out and the solids were mechanically removed.

The liquids extracted from this tank were disposable as oil field wasteunder the EPA solid waste disposal regulations. No waste was classifiedas hazardous waste. The total volume of demulsifiers and liquefactionagents used to treat the sludge was less than 2,100 bbl. This amountedto less than 7% of the total volume of sludge treated. Finally, thetotal down time for the tank was only five days.

Example 3

The invention was used to treat a crude oil storage tank having a totalvolume of approximately 200,000 bbl and containing approximately 7,500bbl of sludge. The sample data taken from the sludge in example one wasused in treating the sludge in this example.

Approximately 450 bbl (˜6% of the sludge volume) of C105 BC were addedto the tank over three hours. Recirculation at approximately 8000 bblper hour was conducted during the introduction of the C105 BC. When allof the C105 BC had been added, approximately 35-40 bbl (˜5000 ppm) ofC105 EB were added to the tank. Recirculation was continued forforty-eight hours at 8000 bbl per hour. At the end of the forty-eighthours, the sludge was liquefied and demulsified.

This former sludge and the C105 BC and C105 EB it contained were pumpedinto a second tank having a total volume of approximately 200,000 bbland containing approximately 2,500 bbl of sludge. No additionalchemicals were added.

The contents of the second tank were circulated for forty-eight hours.At the end of the forty-eight hours, the sludge was liquefied anddemulsified. An oil layer and a water layer having a combined volume ofapproximately 9,800 bbl were pumped off. A solid layer comprisingprimarily sand and anhydrite remained. The solid layer from both tankshad a volume of less than 200 bbl. Waters were of course containedwithin the solid layer. These waters were siphoned out and the solidswere mechanically removed. The liquids extracted from this tank weredisposable as oil field waste under the EPA solid waste disposalregulations. No waste was classified as hazardous waste.

In the foregoing examples, the oils and waters were both disposed of, sotheir individual volumes were not measured; however, an observableseparation was noted in all three tanks. Also, a sample was taken of theliquefied and demulsified oil layer in one tank, and it was found tohave an API (American Petroleum Institute) gravity of 34.6. Thisrelatively high API gravity is indicative of a low water content in theoil layer. In light of this API gravity, the liquids extracted couldhave easily been separated and sent to a refinery for processing.

Separate samples were not taken from the sludge in each tank. Nor werepost liquefaction and demulsification samples taken of the oil layers ineach tank. Ordinarily, this would have been done; however, separatesamples were not needed from each because the tanks in question were allexclusively used to store oil from the same field. Thus, the sludgeswere all expected to be of substantially the same constitution as werethe products produced when those sludges were liquefied and demulsified.

Other uses and embodiments of the invention, equivalent to thatdisclosed herein, will occur to those skilled in the art, and areintended to be included within the scope and spirit of the followingclaims.

What is claimed is:
 1. A liquefaction agent for liquefying hydrocarbonbased sludges comprising: glycol ethers; sodium silicate; water; and anacid of sufficient strength to produce a pH in said liquefaction agentas low as about
 5. 2. A liquefaction agent according to claim 1 whereinsaid glycol ethers comprise at least about five (5) percent by volume ofsaid liquefaction agent.
 3. A liquefaction agent according to claim 1wherein said sodium silicate comprises at least about five (5) percentby volume of said liquefaction agent.
 4. A liquefaction agent accordingto claim 1 wherein said acid is of sufficient strength to produce a pHin said liquefaction agent of between about 5 and about
 6. 5. Aliquefaction agent according to claim 4 wherein said acid comprisescitric acid.
 6. A liquefaction agent according to claim 1 wherein saidglycol ethers are comprised of ethylene glycol butyl ether.
 7. Aliquefaction agent according to claim 6 wherein said ethylene glycolbutyl ether comprises at least about five (5) percent by volume of saidliquefaction agent.
 8. A liquefaction agent according to claim 6 whereinsaid sodium silicate comprises at least about five (5) percent by volumeof said liquefaction agent.
 9. A liquefaction agent according to claim 6wherein said acid is of sufficient strength to produce a pH in saidliquefaction agent of between about 5 and about
 6. 10. A liquefactionagent according to claim 9 wherein said acid comprises citric acid. 11.A liquefaction agent according to claim 1 wherein said glycol ethers arecomprised of polymerized glycol ethers.
 12. A liquefaction agentaccording to claim 11 wherein said polymerized glycol ethers comprise atleast about five (5) percent by volume of said liquefaction agent.
 13. Aliquefaction agent according to claim 11 wherein said sodium silicatecomprises at least about five (5) percent by volume of said liquefactionagent.
 14. A liquefaction agent according to claim 11 wherein said acidis of sufficient strength to produce a pH in said liquefaction agentbetween about 5 and about
 6. 15. A liquefaction agent according to claim14 wherein said acid comprises citric acid.
 16. A liquefaction agentaccording to claim 1 wherein said glycol ethers are comprised of poly(oxy-1,2 ethanediyl) butyl hydroxy.
 17. A liquefaction agent accordingto claim 16 wherein said poly (oxy-1,2 ethanediyl) butyl hydroxycomprises at least about five (5) percent by volume of said liquefactionagent.
 18. A liquefaction agent according to claim 16 wherein saidsodium silicate comprises at least about five (5) percent by volume ofsaid liquefaction agent.
 19. A liquefaction agent according to claim 16wherein said acid is of sufficient strength to produce a pH in saidliquefaction agent between about 5 and about
 6. 20. A liquefaction agentaccording to claim 19 wherein said acid comprises citric acid.